Computer systems use a significant amount of power. Reducing the amount of power used and/or using the power more efficiently helps reduce the cost of operating the computer systems. Operating the computer system more efficiently give the user more results for a given amount of power used. Limiting the peak amount of power used by a computer system is sometimes called power capping. Power capping can reduce the cost of the power and cooling infrastructure by limiting the maximum load that it must support.
Power capping can be done by monitoring the power draw of a computer system. When the power draw exceeds a threshold value, the amount of power used by the system is reduced until the power draw is below the threshold. Typically, one of the main consumers of power in a computer system is the processor. By reducing the clock speed of a processor, the total power used by the computer system may be reduced. in some computer systems, for example blade systems, power capping can he done at a system level, a rack level, a blade level, or at the individual processor level.
In data centers, all the computer systems may not be utilized equally. Some systems may be fully utilized while other systems may be lightly utilized or may be idle. Running a processor at maximum clock speed when the processor is not doing any work is inefficient. Performance management systems monitor the utilization or usage of the computer systems and reduce power to systems that are lightly utilized or are at idle. Performance management systems may reduce power by reducing the clock speed and/or the voltage to processors that are lightly utilized or that are at idle. One example performance management system is disclosed in U.S. Pat. No. 7,536,567 “Bios-based system and method of processor power management” granted May 19, 2009 and which is hereby incorporated by reference for all that it teaches,
Currently the power capping and performance management systems may operate independently, This allows the two systems to be optimized for their particular needs, for example the power capping system typically needs to react much more quickly than the performance management system. Both the power capping and performance management systems use the clock speed of the processor to control the computer systems power usage. When the two systems are operating independently, the two systems may interact and enter an astable state where the power capping system will reduce power to a system by throttling the performance, and the change in performance will cause the performance management system to change states and thus impact the power draw of the system. Oscillation may occur if state changes for both systems are not synchronized and the two cannot agree upon a steady state. In some instances the interaction of the two systems may cause power spikes that exceed the power capping threshold.